Query Active Directory from ASP.NET

[Andrew Connell]

I have a case where I need to be able to query Active Directory to
look up a user by their WINNT:\\DOMAIN\USERACCOUNT. The site is
authenticating the users (it's a CMS site and they must be
authenticated). I have Integrated Authentication & Anon access
checked in IIS. I also have the following in my web.config:
<authentication mode="Windows" />
<identity impersonate="true" />
<trust level="Full" originUrl="" />

However, after building the solution, when I try to create it, I get
the following: "The specified directory service attribute or value
does not exist"

I've copied the lookup code verbatum into a console app and run it
from the same server and it works perfectly (for the same user
lookup)... any ideas why I'm getting this error? It looks security
related, but I'm having a hard time getting the user it's running as
out into my debug info.

Ideas? Thanks in advance.